EP2215241A2

EP2215241A2 - Method for generating biogas

Info

Publication number: EP2215241A2
Application number: EP08857658A
Authority: EP
Inventors: Claus Rückert
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-12-07
Filing date: 2008-11-13
Publication date: 2010-08-11
Anticipated expiration: 2028-11-13
Also published as: WO2009071428A2; ATE502113T1; DE502008002919D1; DE102007059084A1; EP2215241B1; DE102007059084B4; WO2009071428A3

Abstract

The invention relates to a method for generating biogas (B) from a substrate (S1) having a first ammonia-nitrogen concentration of more than 5.0 kg NH 4 -N/m 3, particularly poultry manure, comprising the following steps: producing a fermentation substrate comprising a mixture of the substrate (S1) and a further substrate (S2), determining a second ammonia-nitrogen concentration of the fermentation substrate and adjusting the second ammonia-nitrogen concentration in the fermentation substrate such that it does not drop below a minimum value of 3.0 kg NH 4 -N/m 3, wherein (i) process water (P) extracted from a prefermented digestate and purified by means of a reverse osmosis process is added to the fermentation substrate in order to lower the second ammonia-nitrogen concentration, and (ii) substrate (S1) is added to the fermentation substrate in order to increase the second ammonia-nitrogen concentration.

Description

description

Process for the production of biogas

The invention relates to a method for producing biogas from substrates having a high first ammonium nitrogen concentration, in particular poultry droppings.

DE 10 2005 047 719 A1 discloses a process for the production of biogas from biomass with high solids and nitrogen contents. In this case, a digestate formed during fermentation is separated into two partial streams. A first partial stream is recirculated to mash new biomass. In a stripping process, ammonia / ammonium nitrogen is removed from a second partial stream and then separated into a solid and a liquid phase. The liquid phase is also recirculated to mash new biomass.

The stripping process reduces the ammonia nitrogen content by 70% to 90%. As a result, the recirculated liquid phase of the second substream contains up to 30% ammonium nitrogen. In order to avoid an excessively high content of ammonium in the fermentation substrate and a consequent nitrogen inhibition, in the known method only a relatively small proportion of poultry feces having a high ammonium nitrogen concentration can be added to the fermentation substrate. As a rule, the proportion of poultry feces on the fermentation substrate is not more than 25% by weight.

DE 103 53 728 A1 relates to a process for the production of biogas. Here, a partially fermented substrate is removed from the reactor and separated into a solid and a liquid phase. The liquid phase is separated by a stripping essentially free of ammonia and ammonia. The liquid phase is then mixed with the solid phase in a mixing vessel. 40 to 80% by volume of the solid / liquid mixture are returned to the reactor.

From EP 1 762 607 Al a control method for biogas plants is known. The ammonia value of a fermentation substrate is maintained at a predetermined desired value by adding appropriate control substrates. The return of a processed fermentation residue in the biogas reactor is not provided.

DE 10 2004 030 482 A1 relates to a process for the treatment of waste water from the processing and treatment of organic waste, in particular manure, with a biogas fermenter. Fermenter residues are removed from the fermenter and subjected to a solid-liquid separation. Part of the solid phase is recycled to the fermenter. The liquid phase is subjected to ultrafiltration and reverse osmosis. The purified liquid phase is partially recycled to the fermenter. The aim of the method is the production of a einleitfähigen, especially agriculturally usable, water.

From DE 10 2004 003 458 Al a method for processing residual waste is known. The denitrification of a process water takes place by means of a stripping device.

Currently, prices for renewable raw materials are rising sharply due to rising demand. On the other hand, because of its high nitrogen content, poultry droppings are generally not easy to dispose of and are therefore given free of charge. The object of the present invention is to provide a method which is as simple and inexpensive as possible for obtaining biogas from fermentation substrates having a high content of ammonium nitrogen, in particular poultry feces.

This object is solved by the features of claim 1. Advantageous embodiments emerge from the features of claims 2 to 19.

According to the invention, a method for producing biogas from a substrate having a first ammonium nitrogen concentration of more than 5.0 kg NH ₄ -N / m ³ , in particular poultry feces, is provided with the following steps:

Producing a fermentation substrate containing a mixture of the substrate and another substrate,

Determining a second ammonium nitrogen concentration of the fermentation substrate and

Setting the second ammonium nitrogen concentration in the fermentation substrate in such a way that a minimum value of 3.0 kg NH ₄ -N / m ³ is not fallen below and a maximum value of 5.5 kg NH ₄ -N / m ³ is not exceeded, wherein the fermentation substrate

(I) for lowering the second ammonium nitrogen concentration of a fermented digestion withdrawn and purified by a reverse osmosis process and process water

(ii) to increase the second ammonium nitrogen concentration of the first substrate is added.

With the proposed method, it is possible to ferment fermentation substrates with a high proportion of substrates having a high first ammonium nitrogen concentration, in particular poultry droppings. In contrast to the prior art, it is thus possible to convert fermentation substrates with a proportion of more than 30% by weight of poultry droppings into biogas. According to the invention, this is achieved in particular by a suitable adjustment of the second ammonium nitrogen concentration in the fermentation substrate. In this case, for particularly efficient processing of the substrate, the second ammonium nitrogen concentration is preferably set close to the maximum value, for example in a range of more than 4.0 kg NH ₄ -N / m ³ to 5.5 kg NH ₄ -N / m ³ . A particularly preferred range of the second ammonium nitrogen concentration ranges from a minimum value of 4.5 kg NH ₄ -N / m ³ to a maximum value of 5.5 kg NH ₄ -N / m ³ .

To set the aforementioned ranges of the second ammonium nitrogen concentration, it may either be necessary to lower or to increase the second ammonium nitrogen concentration. According to the invention, to reduce the second ammonium nitrogen concentration, a process water withdrawn from fermented digestate and purified by means of a reverse osmosis process is added. Such process water has an extremely low ammonium concentration. In any case, it is so clean that it can be disposed of by discharge into receiving waters or into rivers. By using process water to lower the second ammonium nitrogen concentration, on the one hand the consumption of valuable fresh water can be avoided and on the other hand an entry of ammonium into the fermentation substrate can be avoided. As a result, can the fermentation substrate, a particularly high proportion of substrate or poultry droppings are added.

For setting the above range of the second ammonium nitrogen concentration, it may also be necessary to increase it. For this purpose substrate is added to the fermentation substrate. Since the substrate generally has a first ammonium nitrogen concentration of more than 5.0 kg NH ₄ -N / m ³ , in particular more than 10.0 kg NH ₄ -N / m ³ , can thus the second ammonium nitrogen concentration increases and at the same time an efficient disposal of the substrate can be achieved.

According to an advantageous embodiment, the ammonium content or the ammonia content in the fermentation substrate is measured to determine the second ammonium nitrogen concentration. In that regard, known prior art measuring devices can be used. Advantageously, the second ammonium nitrogen concentration is continuously measured and monitored by means of known measuring devices.

Similarly, the first ammonium nitrogen concentration in the substrate can also be determined. Also for this purpose, the ammonium content or the ammonia content in the substrate can be measured. In this case, the substrate is in a separate reservoir.

According to a particularly advantageous further embodiment, it is provided that the first ammonium nitrogen concentration is reduced to a predetermined value by heating the substrate prior to addition to the fermentation substrate. In this case, the predetermined value as a function of the second ammonium nitrogen concentration and the amount of the fermentation substrate and the Amount of the substrate to be determined. For heating the substrate can advantageously be used by burning biogas produced exhaust gas. Biogas can be burned to drive a generator, for example. - By the proposed heating of the substrate to a temperature, for example in the range of 50 ⁰ C to 100 ⁰ C therein contained ammonium is removed in the form of ammonia. Thus, the first ammonium nitrogen concentration can be easily adapted to the respective requirements. The respective requirements are influenced by the amount of the fermentation substrate, the second ammonium nitrogen concentration, an amount of a further substrate and the nature of the further substrate.

Usually, a third ammonium nitrogen concentration of the further substrate is smaller than the first ammonium nitrogen concentration. As a result, the second ammonium nitrogen concentration can also be reduced by the nature of the further substrate and its proportion in the fermentation substrate. The further substrate can essentially be formed from renewable vegetable raw materials or biogenic residues. Since the method according to the invention is directed in particular to an efficient disposal of substrates containing nitrogen, in particular poultry feces, the second ammonium nitrogen concentration in the fermentation substrate is usually first lowered by adding process water. If the predetermined range of the second ammonium nitrogen concentration is thus not reached, a further reduction can be achieved by heating the substrate and / or by mixing the substrate with the further substrate. According to a further embodiment of the invention, it is provided that for the preparation of the digestate from the fermentation substrate settling sediment is suspended by means of a reel agitator in the fermented fermentation substrate. Such a suspended fermentation residue can be removed by means of a pump from a fermentation reactor. This enables a particularly simple process control.

According to a further embodiment feature, solids contained in the digestate in a further process step are separated by means of microfiltration, preferably ultrafiltration. The pellets produced in this way form a valuable free-flowing dry fertilizer.

According to a further advantageous embodiment, the reverse osmosis process is a multi-stage process in which advantageously a first reverse osmosis and subsequently a second reverse osmosis is carried out.

Advantageously, a portion of a residual liquid remaining after separation of the solids from the digestate can be withdrawn and used as a liquid fertilizer or for its production. The residual liquid is subsequently advantageously further purified by means of the reverse osmosis process. On the one hand, purified process water is obtained, which is used to adjust the second ammonium nitrogen concentration. Furthermore, this results in a further residual liquid, which in turn can be used as a liquid fertilizer or for its production.

If, in accordance with the aforementioned embodiment, residual liquid and / or further residual liquid are removed from the process, it is expedient to remove approximately the volume of the liquid which has been removed. the residual liquid and / or other residual liquid corresponding volume of liquid added to the fermentation substrate. In this case, water used as liquid in the substrate or in the further substrate can be used. If this water is insufficient, a possibly remaining difference volume can be compensated by the addition of further liquid, preferably fresh water, residual water or wastewater. For example, as residual water in fruit juice production sloping liquids or the like. used to compensate for the difference volume.

An embodiment of the invention will be explained in more detail with reference to the drawing.

The single drawing shows schematically a procedure. Poultry manure with a first ammonium nitrogen concentration of more than 5.0 kg NH ₄ -N / m ³ , preferably more than 10.0 kg NH ₄ -N / m ³ , is used as substrate Sl. As a further substrate S2, biogenic residues, for example corn or the like, are used. Their second ammonium nitrogen concentration is less than the first ammonium nitrogen concentration. It is usually less than 3.0 kg NH ₄ -N / m ³ . The first substrate Sl and the further substrate S2 are placed in a mixer 1. There, a mixture is prepared which contains at least 30% by weight of the first substrate S1 and at most 70% by weight of the second substrate S2. The mixture is thoroughly mixed in the mixer 1 and homogenized by adding fresh water and / or process water and / or residual liquid. The result is a creamy, flowable and thus pumpable mass with a dry matter content (TS) in the range of 10 to 25 wt .-%, preferably 15 to 25 wt .-%. For the purposes of the present invention, the term "homogeneous mixture" means a mixture of understood in which the poultry faeces is substantially completely dispersed. That is, the poultry feces are present in the mixture in a proportion of more than 90% in a mean grain size of less than 5 mm.

If necessary, the substrate Sl may be heated prior to addition to the mixer 1 to lower the first ammonium nitrogen concentration. In this case, heat can be used to heat the substrate Sl, which is decoupled, for example, from a biogas-operated cogeneration plant. As a result of the heat treatment liberated ammonia is fed to neutralize a neutralizer 2. This may be an acid scrubber, for example a sulfuric acid scrubber.

For the preparation of a fermentation substrate, process water P and, if necessary, additional fresh water F are added to the mixture. After setting a suitable consistency, the fermentation substrate thus prepared is transferred in a reactor 3. In this case, an ammonium nitrogen concentration in the reactor 3, preferably continuously, determined and regulated, so that a minimum concentration of 3.0 kg NH ₄ -N / m ³ not lower and a maximum concentration of 6.5 kg NH ₄ - N / m ^{3 is} not exceeded. To maintain the aforementioned concentration range, fermentation substrate is supplied to a suitable ammonium nitrogen concentration. The H ₂ S concentration is expediently set in the reactor 3 so that it does not exceed a value of 100 mg / l.

For suspending solids in the reactor 3, a reel mixer 4 is provided. The reference symbol B denotes biogas, which is formed when the fermentation substrate is fermented is discharged and discharged from the reactor 3 to generate energy.

As soon as the fermentation substrate is substantially fermented, it is suspended by means of the coiler agitator 4 and introduced into a downstream liquid / solid phase separation device 5, e.g. As a decanter, pumped. There, the substantially fermented fermentation substrate is separated into a solid phase and a liquid phase.

The liquid phase is purified by ultrafiltration UF and then subjected to a, preferably two-stage, reverse osmosis UO. After performing a first reverse osmosis stage, a liquid phase is generated which can be decoupled from the process and used as liquid fertilizer.

After performing a second reverse osmosis stage process water P accumulates, which is supplied to the mixer 1 for the production of the fermentation substrate. Excess process water P can be withdrawn from the process if necessary.

The solids withdrawn from the liquid / solid phase separation device 5 can be dried and subsequently pelletized. They can either be used as fertilizer, composted or even burned.

Reference sign list

1 mixer

2 neutralizer 3 reactor

4 reel agitator

Liquid / solid phase separator

B biogas

F fresh water

P process water

Sl substrate

S2 further substrate

UF ultrafiltration

UO reverse osmosis

Claims

claims

1. A process for the production of biogas (B) from a substrate (Sl) having a first ammonium nitrogen concentration of more than 5.0 kg NH ₄ -N / m ^3, in particular poultry manure, comprising the steps of:

Producing a fermentation substrate containing a mixture of the substrate (S1) and further substrate (S2),

(i) for lowering the second ammonium nitrogen concentration, a process water (P) extracted from a fermented fermentation residue and purified by a reverse osmosis process;

(ii) for increasing the second ammonium nitrogen concentration to the fermentation substrate (S1)

is added.

2. The method of claim 1, wherein for determining the second ammonium nitrogen concentration, the ammonium content or the ammonia content in the fermentation substrate is measured.

3. The method according to any one of the preceding claims, wherein the first ammonium nitrogen concentration in the substrate (Sl) is determined.

4. The method according to any one of the preceding claims, wherein for determining the first ammonium nitrogen concentration, the ammonium content or the ammonia content in the substrate (Sl) is measured.

5. The method according to any one of the preceding claims, wherein the first ammonium nitrogen concentration is reduced by heating the substrate (Sl) before addition to the fermentation substrate to a predetermined value.

6. The method according to any one of the preceding claims, wherein the predetermined value as a function of the second ammonium nitrogen concentration and the amount of the fermentation substrate and the amount of the substrate (Sl) is determined.

7. The method according to any one of the preceding claims, wherein for heating the substrate (Sl) by burning biogas (B) generated exhaust gas is used.

8. The method according to any one of the preceding claims, wherein a third ammonium nitrogen concentration of the other

Substrate (S2) is less than the first ammonium nitrogen concentration.

9. The method according to any one of the preceding claims, wherein the further substrate (S2) is formed essentially of renewable vegetable raw materials or biogenic residues.

10. The method according to any one of the preceding claims, wherein for the preparation of the digestate from the fermentation substrate settling sediment is suspended by means of a reel mixer (4) in the fermented fermentation substrate.

11. The method according to any one of the preceding claims, wherein the digestate is removed by means of a pump from a fermentation reactor (3).

12. The method according to any one of the preceding claims, wherein solids contained in the digestate are separated by microfiltration, preferably by ultrafiltration (UF).

13. The method according to any one of the preceding claims, wherein the separated solids are composted or pelletized.

14. The method according to any one of the preceding claims, wherein in the reverse osmosis method, a first reverse osmosis and subsequently a second reverse osmosis is performed.

15. The method according to any one of the preceding claims, wherein a portion of a remaining after separation of the solids from the digestate remaining liquid withdrawn and used as a liquid fertilizer or for its production.

16. The method according to any one of the preceding claims, wherein the residual liquid purified by means of the reverse osmosis method and a further residual liquid formed thereby is used as a liquid fertilizer or for its production.

17. The method according to any one of the preceding claims, wherein an approximately the volume of the withdrawn residual liquid and / or further residual liquid corresponding volume of liquid (F, P) is added to the fermentation substrate.

18. The method according to any one of the preceding claims, wherein as a liquid in the substrate (Sl) or in the further substrate

(S2) contained water is used.

19. The method according to any one of the preceding claims, wherein a possibly remaining difference volume by the addition of further terer liquid, preferably fresh water (F), residual water or wastewater, is compensated.